This invention relates to an acoustooptic deflection device for use in deflecting a light beam by the use of an acoustic wave.
A conventional acoustooptic deflection device of the type described deflects a light beam by making use of Raman-Nath or Brillouin scattering, as well known in the art. For this purpose, the acoustooptic deflection device comprises an acoustooptic medium supplied with the light beam and a transducer attached to the acoustooptic medium. Responsive to an electric signal, the transducer generates an acoustic or ultrasonic wave directed to the acoustooptic medium. The acoustic wave interacts with the light beam in the acoustooptic medium so as to deflect the light beam by a deflection angle and to produce a deflected light beam. Such a deflection angle is variable in dependence on the frequency of the electric signal.
It is preferable that the deflection angle is as large as possible to raise a resolution of the deflected light beam and that luminous energy of the deflected light beam is invariable.
In order to expand the deflection angle, the frequency of the electric signal should be varied over a wide frequency band. However, it is impossible to match an input impedance of the transducer to a predetermined value of, for example, 50 ohms in such a wide frequency band. Accordingly, a reflection loss inescapably becomes large and deflection efficiency, namely, the luminous energy of the deflected light beam is objectionably reduced in the conventional acoustooptic deflection device.
In the copending U.S. patent application Ser. No. 517,346 filed on July 26, 1983, by S. Amano et al, now U.S. Pat. No. 4,592,621, an acoustooptic modulation device is proposed which comprises a single acoustooptic medium for individually deflecting a plurality of light beams by acoustic waves produced from a plurality of transducers, respectively. The transducers are activated by carrier waves each of which has a single carrier frequency and which are individually subjected to modulation. Consideration may be made about applying such an acoustooptic modulation device to the acoustooptic deflection device as mentioned above. However, such application brings about an increase of reflection losses because the frequency of the electric signal should widely be varied in the acoustooptic deflection device.